The teachings of all of the references cited herein are incorporated in their entirety by reference.
A major disadvantage of drug administration by injection is that trained personnel are often required to administer the drug. For self-administered drugs, many patients are reluctant or unable to give themselves injections on a regular basis. Injection is also associated with increased risks of infection. Other disadvantages of drug injection include variability of delivery results between individuals, as well as unpredictable intensity and duration of drug action.
Despite these noted disadvantages, injection remains the only approved delivery mode for a many important therapeutic compounds. These include conventional drugs, as well as a rapidly expanding list of peptide and protein biotherapeutics. Delivery of these compounds via alternate routes of administration, for example, oral, nasal and other mucosal routes, often yields variable results and adverse side effects, and fails to provide suitable bio-availability. For macromolecular species in particular, especially peptide and protein therapeutics, alternate routes of administration are limited by susceptibility to inactivation and poor absorption across mucosal barriers.
Mucosal administration of therapeutic compounds may offer certain advantages over injection and other modes of administration, for example in terms of convenience and speed of delivery, as well as by reducing or elimination compliance problems and side effects that attend delivery by injection. However, mucosal delivery of biologically active agents is limited by mucosal barrier functions and other factors. For these reasons, mucosal drug administration typically requires larger amounts of drug than administration by injection. Other therapeutic compounds, including large molecule drugs, peptides and proteins, are often refractory to mucosal delivery.
The ability of drugs to permeate mucosal surfaces, unassisted by delivery-enhancing agents, appears to be related to a number of factors, including molecular size, lipid solubility, and ionization. Small molecules, less than about 300-1,000 Daltons, are often capable of penetrating mucosal barriers, however, as molecular size increases, permeability decreases rapidly. Lipid-soluble compounds are generally more permeable through mucosal surfaces than are non-lipid-soluble molecules. Peptides and proteins are poorly lipid soluble, and hence exhibit poor absorption characteristics across mucosal surfaces.
In addition to their poor intrinsic permeability, large macromolecular drugs, including proteins and peptides, are often subject to limited diffusion, as well as lumenal and cellular enzymatic degradation and rapid clearance at mucosal sites. These mucosal sites generally serve as a first line of host defense against pathogens and other adverse environmental agents that come into contact with the mucosal surface. Mucosal tissues provide a substantial barrier to the free diffusion of macromolecules, while enzymatic activities present in mucosal secretions can severely limit the bioavailability of therapeutic agents, particularly peptides and proteins. At certain mucosal sites, such as the nasal mucosa, the typical residence time of proteins and other macromolecular species delivered is limited, e.g., to about 15-30 minutes or less, due to rapid mucociliary clearance.
In summary, previous attempts to successfully deliver therapeutic compounds, including small molecule drugs and protein therapeutics, via mucosal routes have suffered from a number of important and confounding deficiencies. These deficiencies point to a long-standing unmet need in the art for pharmaceutical formulations and methods of administering therapeutic compounds that are stable and well tolerated and that provide enhanced mucosal delivery, including to targeted tissues and physiological compartments such as central nervous system. More specifically, there is a need in the art for safe and reliable methods and compositions for mucosal delivery of therapeutic compounds for treatment of diseases and other adverse conditions in mammalian subjects. A related need exists for methods and compositions that will provide efficient delivery of macromolecular drugs via one or more mucosal routes in therapeutic amounts, which are fast acting, easily administered and have limited adverse side effects such as mucosal irritation or tissue damage.
In relation to these needs, an especially challenging need persists in the art for methods and compositions to enhance mucosal delivery of biotherapeutic compounds that will overcome mucosal epithelial barrier mechanisms. Selective permeability of mucosal epithelia has heretofore presented major obstacles to mucosal delivery of therapeutic macromolecules, including biologically active peptides and proteins. Accordingly, there remains a substantial unmet need in the art for new methods and tools to facilitate mucosal delivery of biotherapeutic compounds. In particular, there is a compelling need in the art for new methods and formulations to facilitate mucosal delivery of biotherapeutic compounds that have heretofore proven refractory to delivery across mucosal barriers.